# Issue with modbus data **URL:** \ **Category:** Ignition\ **Created:** [August 2, 2024, 3:23pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118 "2024-08-02T15:23:53Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![PRASHANTH\_KAKKIRALA](https://avatars.discourse-cdn.com/v4/letter/p/76d3ee/32.png) [@PRASHANTH\_KAKKIRALA](https://forum.inductiveautomation.com/u/PRASHANTH_KAKKIRALA)\ **Post date:** [August 2, 2024, 3:23pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/1 "2024-08-02T15:23:53Z")
What can cause this? Read shows correct values but subscribe is not? ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/2/c/2ca7e21f6a3834083b9be1edd7e1883ef651ed9f.png) ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [August 2, 2024, 3:26pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/2 "2024-08-02T15:26:08Z")
Maybe start with a Wireshark capture. It would also be useful to see your Modbus Address mapping configuration (though I recommend you don't use that at all if you can avoid it). ---
**Author:** ![PRASHANTH\_KAKKIRALA](https://avatars.discourse-cdn.com/v4/letter/p/76d3ee/32.png) [@PRASHANTH\_KAKKIRALA](https://forum.inductiveautomation.com/u/PRASHANTH_KAKKIRALA)\ **Post date:** [August 2, 2024, 3:31pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/3 "2024-08-02T15:31:08Z")
Here is the mapping configuration ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/4/d/4d7a99efb9f497208f73e6306876a9ecd4f315bc.png) ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [August 2, 2024, 3:32pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/4 "2024-08-02T15:32:25Z")
Ok, now with both of those tags still subscribed in the Quick Client, start a Wireshark capture, then initiate a read for the single tag. Both requests should be in the capture. Upload it here. ---
**Author:** ![PRASHANTH\_KAKKIRALA](https://avatars.discourse-cdn.com/v4/letter/p/76d3ee/32.png) [@PRASHANTH\_KAKKIRALA](https://forum.inductiveautomation.com/u/PRASHANTH_KAKKIRALA)\ **Post date:** [August 2, 2024, 4:01pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/5 "2024-08-02T16:01:45Z")
![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/0/c/0c01271f9b055889672600e4b2d3d37a88bab8a5.png) ---
**Author:** ![michael.flagler](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/michael.flagler/32/26272_2.png) [@michael.flagler](https://forum.inductiveautomation.com/u/michael.flagler)\ **Post date:** [August 2, 2024, 4:07pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/6 "2024-08-02T16:07:40Z")
You need to save the PCAP file and upload that. A screenshot does no good. ---
**Author:** ![PRASHANTH\_KAKKIRALA](https://avatars.discourse-cdn.com/v4/letter/p/76d3ee/32.png) [@PRASHANTH\_KAKKIRALA](https://forum.inductiveautomation.com/u/PRASHANTH_KAKKIRALA)\ **Post date:** [August 2, 2024, 4:12pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/7 "2024-08-02T16:12:40Z")
[Analysis.pcapng](https://forum.inductiveautomation.com/uploads/short-url/dkZLo3pB2r7aSt8OPOGyj2GieM2.pcapng) (2.1 MB) Here is the file Modbus device address: 10.175.133.38 ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [August 2, 2024, 4:18pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/8 "2024-08-02T16:18:02Z")
I don't see anything strange, but in this capture the single read you did looks to have been for "OPA1" and not "OPA3" like in your screenshot. ---
**Author:** ![PRASHANTH\_KAKKIRALA](https://avatars.discourse-cdn.com/v4/letter/p/76d3ee/32.png) [@PRASHANTH\_KAKKIRALA](https://forum.inductiveautomation.com/u/PRASHANTH_KAKKIRALA)\ **Post date:** [August 2, 2024, 4:20pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/9 "2024-08-02T16:20:50Z")
[Analysis.pcapng](https://forum.inductiveautomation.com/uploads/short-url/bWPhVGFaI3uTY5YZKw1N9KrhCCp.pcapng) (3.3 MB) I clicked on both tags reads in this ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [August 2, 2024, 4:24pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/10 "2024-08-02T16:24:13Z")
Your device seems to return different data for the same registers depending on how many overall register are being read. Reading Input Registers 0-7: ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/9/b/9b9f94014d4ff209d0bda0fa6d82f6b8066e7231.png) Reading Input Registers 2-3: ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/8/0/808c6c4e38d351631fc4a47cf097056fbea46731.png) Note the different values returned for 2 and 3 between the two screenshots... Seems like you should be talking to the vendor of this device about its buggy implementation. ---
**Author:** ![PRASHANTH\_KAKKIRALA](https://avatars.discourse-cdn.com/v4/letter/p/76d3ee/32.png) [@PRASHANTH\_KAKKIRALA](https://forum.inductiveautomation.com/u/PRASHANTH_KAKKIRALA)\ **Post date:** [August 2, 2024, 4:31pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/11 "2024-08-02T16:31:11Z")
Ok. What is the reason for change in values when we click on 'read' and 'subscribe' ? ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/7/e/7e76b49186aa768cfb523c4b78a832bbb01023fb.png) ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [August 2, 2024, 4:34pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/12 "2024-08-02T16:34:57Z")
When you click Read it sends a request for just the 2 registers needed for that tag. With your subscribed tags, all 8 of the sequential registers needed are bundled into a single request. ---
**Author:** ![PRASHANTH\_KAKKIRALA](https://avatars.discourse-cdn.com/v4/letter/p/76d3ee/32.png) [@PRASHANTH\_KAKKIRALA](https://forum.inductiveautomation.com/u/PRASHANTH_KAKKIRALA)\ **Post date:** [August 2, 2024, 5:14pm UTC](https://forum.inductiveautomation.com/t/issue-with-modbus-data/94118/13 "2024-08-02T17:14:08Z")
I split the definition into multiple address mapping categories and that seemed to work.